This invention relates to a carburetor for an automotive internal combustion engine and, more particularly, to improvements of an acceleration pump for the carburetor.
Conventional acceleration pumps are generally classified as a piston type or a diaphragm type. As shown in FIG. 3, which illustrates a conventional piston type acceleration pump provided in a carburetor in cross section, with piston type acceleration pump 20 is provided with its piston 21 telescopically inserted into a cylinder 27 perforated at part of a float chamber 19. This piston 21 is connected directly to a pump rod 22 at one end and further engaged through a pump lever 26 rockably secured to a carburetor body 31, an acceleration rod 25 connected at one end to the pump lever 26, and a throttle lever 24 connected at one end to the acceleration rod 25 with a throttle valve 23 rockably installed within a barrel of the carburetor.
The cylinder 27 is provided with an inlet valve 28 at an inlet passage as a check valve and also with an outlet valve 29 at an outlet passage.
When the throttle valve 23 is opened in a manner publicly known in the conventional carburetor, the piston 21 of the acceleration pump 20 is cooperatively telescopically moved via the linkage of the throttle lever 24, the acceleration rod 25, the pump lever 26, and the pump rod 22 by means of the tension of a coil spring inserted into the cylinder 27. Fuel is injected into the cylinder 27 through the outlet passage, and the outlet valve 29 from an acceleration nozzle 30 protruded into the barrel of the carburetor body 31 into an air intake opening 32, preventing temporary decreasing of the air/fuel ratio of the air/fuel mixture and deterioration of the acceleration of this vehicle due to delayed fuel increase caused by the abrupt increase of intake air stream within the opening 32 when the throttle valve 23 is abruptly opened.
As shown further in FIG. 4, which illustrates a conventional diaphragm type acceleration pump provided in a carburetor in cross section, a diaphragm type acceleration pump 33 is provided with diaphragm 34 expansibly movably mounted within a bore perforated in a carburetor body 31 adjacent to a float chamber 19. This diaphragm 34 is connected directly to a pump rod 35 at one end and further engaged through a pump lever 26 rockably secured to a carburetor body 31, an acceleration rod 25 connected at one end to the pump lever 26, and a throttle lever 24 connected at one end to the acceleration rod 25 with a throttle valve 23 rockably installed within a barrel of the carburetor.
A pump chamber 36 formed within the bore of the carburetor body 31 is provided with an inlet valve 28 in an inlet passage 37 as a check valve and also with an outlet valve 29 in an outlet passage 38, and communicates through the inlet passage with the float chamber 19.
When the throttle valve 23 is opened in a manner generally known in the conventional carburetor, the diaphragm 34 of the accelerator pump 33 is cooperatively expansibly moved through the linkage of the throttle lever 24, the acceleration rod 25, the pump lever 26 and the pump rod 35 against the tension of a diaphragm coil spring 40 inserted into the pump chamber 36 between the bottom of the pump chamber 36 and the diaphragm 34. Thus, fuel is injected into the pump chamber 36 through the outlet passage 38 and the outlet valve 29 from an acceleration nozzle 30 protruded into the barrel of the carburetor body 31 into an air intake opening 32 of the carburetor body 31, thereby preventing the air/fuel ratio of the air/fuel mixture from temporarily decreasing and deteriorating the acceleration of this vehicle due to delayed fuel increase caused by the abrupt increase of intake air stream within the opening 32 when the throttle valve 23 is abruptly opened. An atmospheric air chamber 39 is formed at the outside of the diaphragm 34 and accordingly at the opposite side of the pump chamber 36 in the acceleration pump 33. The pump lever 26 is rockably secured to a fulcrum 41 of the carburetor body 31.
The conventional acceleration pump of both the types incorporates the single pump lever 26 to inject fuel only a short time when the piston 21 of the acceleration pump 20 is pushed down or the diaphragm 34 of the acceleration pump 33 is moved toward the bottom side of the pump chamber 36 leftwardly in FIG. 4 as designated by broken curve A of FIG. 5. Thus fuel is temporarily injected excessively in the amount of fuel flow as indicated by Q.sub.1 which is temporarily more than the maximum fuel flow (as designated by Q.sub.5 in FIG. 7). Accordingly, this injecting time is too short to compensate the decrease of the air/fuel rario of the air/fuel mixture. In addition, excessive fuel flow is injected temporarily from the acceleration nozzle 30 into the air intake opening 32 of the carburetor, thereby causing deterioration of exhaust gas purification due to unburned gas exhaust, resulting in an increase of fuel consumption.
As shown by curve M in FIG. 8, an automotive engine is abruptly accelerated from the operating state of predetermined air/fuel ratio R with the result that, when the throttle valve is abruptly opened, air stream amount is rapidly increased to increase the negative pressure or vacuum in the air intake opening of the carburetor. Accordingly, fuel is instantaneously taken from a main nozzle into the air/fuel mixture in the air intake opening of the carburetor to cause the air/fuel ratio of the air/fuel mixture to become rich, but not to continuously become rich. The fuel is then delayed, causing the air/fuel ratio of the air/fuel mixture to then become lean, thus allowing the fuel to increasingly inject from the main nozzle gradually to return the fuel to predetermined air/fuel ratio R. This takes several seconds and accordingly insufficient power of the automotive engine is introduced due to the lean air/fuel ratio during this short time and therefore insufficient torque of the engine, causing deterioration of acceleration during this short time.
When the fuel flow injection from the acceleration nozzle shown by curve A in FIG. 5 is superimposed with that from the main nozzle in the carburetor as shown in FIG. 8, an air/fuel ratio becomes as designated by a curve a of broken line to slightly compensate the lean air/fuel ratio of the air/fuel mixture immediately after the acceleration of the automotive engine.
After this acceleration pump is, however, operated, the air/fuel ratio of the air/fuel mixture is temporarily excessively increased. In addition, the curve a in FIG. 8 is remarkably decreased in air/fuel ratio from predetermined value R to thus introduce temporarily lean air/fuel ratio of the air/fuel mixture to cause the fuel flow in the acceleration pump to decrease as shown from the curve a to a curve l. In order to compensate this lean air/fuel ratio of the air/fuel mixture, it is proposed to provide an auxiliary acceleration pump having a diaphragm operated by a vacuum in the air intake opening in addition to the above acceleration pump. This auxiliary acceleration pump operates as designated by curve B in FIG. 5 to inject fuel of small amount Q.sub.2 for a longer time t.sub.2 so as to compensate the lean air/fuel ratio of the air/fuel mixture as shown by curve b in FIG. 8 by superimposing curve M therewith. Thus, the acceleration pump can improve the performance of the carburetor to the vicinity of the predetermined air/fuel ratio R by superimposing the curve a with the curve b in FIG. 8 in incorporation of the auxiliary acceleration pump. When the curve l is superimposed with the curve b in FIG. 8, it can provide an ideal fuel flow curve as shown in FIG. 7.
Although the deterioration of the acceleration of an automotive engine is improved by the incorporation of the auxiliary acceleration pump with the conventional acceleration pump, it causes complicated construction and accordingly intricate adjustment and maintenance.
There is proposed another type of auxiliary means for utilizing fluid pressure of a flow control valve, (cushion chamber, etc.) in the conventional acceleration pump which operates as designated by a fuel flow curve A in FIG. 5 to adjust the total fuel injection amount of the acceleration nozzle to obtain a fuel injection time in the relationship of t.sub.1 &lt;t.sub.3 &lt;t.sub.4 while injecting the fuel in the relationship of Q.sub.1 &gt;Q.sub.3 &gt;Q.sub.4 as shown by the curve A to curve C and D in FIG. 6. It is still insufficient due to the lack of fuel flow increase at the start as compared with an ideal fuel flow shown in FIG. 7.